Wednesday, June 18, 2014

Positioned for Speed

Last week I had the pleasure of co-delivering the first "Positioned for Speed" Course held in Australia, which is part of Retül University's growing list of international course offerings. Many thanks to Matt and Nick at Retül and Andy and the guys at Alphamantis for the opportunity, it was a lot of fun. Looking forward to doing more of them (if they'll have me back that is!).

The two day course was aimed at bike fitters and coaches primarily, and gave attendees an introduction to the theory of aerodynamics relevant to cycling, an understanding of how the theory applies to the practical considerations of bike fitting, what elements of aerodynamics we can influence and improve, how we quantify the impact to performance, as well a chance to design and conduct an aero testing session with a test subject.

I had fun explaining the theoretical aspects, then helping the participants understand and experience exactly how to translate these into actual testing scenarios, and using the Alphamantis track aero testing technology to measure the impact they have on a rider's performance.

We tested bike position options, equipment options (helmets and wheels), body shaping options while riding, and clothing options. Over the course of the session, incremental improvements in the rider's aerodynamics were identified, all while ensuring the rider's position was still bio-mechanically effective and comfortable for the rider when considering the events they are targeting.

Thought I'd share a few examples of comparison test results along the way. I can't say much about the rider, or the exact details of each options tested, but suffice to say they are targeting road time trials and track endurance events.

Put a lid on it


Aero helmets are known to give good aerodynamic benefit but which helmet is best for any individual is quite variable. In any case, the team immediately saw the sizeable benefit of one aero lid over the rider's existing standard "mass start" helmet. These were not the only options tested but just shown as a comparison example.


Putting that into perspective, at this rider's Function Threshold Power, that's a gain of more than 0.6km/h or 1.1 seconds per kilometre on flat road terrain. Some people will gain more speed and some less from an aero helmet, and no one helmet brand or model is the best choice for every rider. Some provide more speed gains than others.

The value of a good shrug


Next example is how you can gain speed by "shrugging" (or "turtling") such that you bring your head down and narrow your shoulders while riding in the TT position, but do so without compromising your power output. Sometimes riders learn to be able to do this for extended periods of time, but it's a technique mainly for shorter road TTs and individual pursuit, not so much for the Ironman athletes out there. The gains can be well worth it if you are able to hold onto a shrug for a while.


In this rider's case, they can increase road time trial speed by nearly 0.5km/h or gain nearly 0.9 seconds per km while they shrug. For some riders there are bike position set ups and helmets that enable the rider to shrug more easily or hold it for longer. Ideally you'd like to set up the bike such that the effect is a full time enhancement, however this is not always feasible, so being on the lookout for more free speed-gaining opportunities is worth a go.

Skinsuits. Choose wisely.


The final example I thought I'd share from the testing session was some skinsuit options. Here we can see the difference between three suits tested.


The best suit is about 0.4km/h or 0.6 seconds per km faster than the team issue suit at this rider's pursuit power on a track. That gives them a 25 metre lead over the slower suit by lap 12.

Overall we identified a 0.033m^2 reduction in this rider's coefficient of drag area, which is equivalent to a 35 watt power saving, or a little over 3 seconds per km or a speed gain of 1.7 km/h.

Talk about a winning margin.

Discussing track test routine with one of the course participants.

Read More......

Saturday, May 31, 2014

Swings and Roundabouts

Today I thought I'd look at how rider's relative abilities play out in Grand Tour stage racing. I was prompted to do so after watching this year's Giro d'Italia's Stage 19 mountain individual time trial.

It's no surprise that to be competitive on general classification (GC) in a grand tour requires, amongst a variety of traits, phenomenal physiological capabilities, and each rider has their strengths and weaknesses relative to their opponents. Clearly climbing ability is a key factor in success, but also a rider's ability in individual time trials (ITT) is also an important factor for success.

Success in the ITT, is more suited to those riders with the highest sustainable power to aerodynamic drag ratio (power to CdA, W/m^2), while climbing steeper gradients a rider's sustainable power to weight ratio (W/kg) is the dominant factor for success.

Some riders are a bit larger and have more power and are relatively more aerodynamically shaped and set up, while others have better power to weight ratios. If you can nearly equal your opponents in one discipline and beat them in the other, then you're well on your way to GC success.

The balance between these two key attributes does vary from race to race as grand tours vary the total number and distance of ITTs, and the number of mountain top finishes. While total metres climbed during a grand tour is a factor for overall fatigue levels, it's the summit finishes and individual time trials that account for the majority of time gained and lost between leading contenders, and these are the critical stages for GC riders.

As an example of this game of physical swings and roundabouts, note the differences in make up of race defining stages in recent editions of the Tour de France:


We can see that the 2012 TdF was far more suited to TT ability than it was for climbing ability, but this year is more weighted towards the climbers. Of course you can't badly falter in either discipline, but 2012 was never one for a pure lightweight climber.

In this 2014 edition of the Giro d'Italia, there have been three time trials: a team time trial, an individual time trial over flat/lumpy terrain and an individual time trial (MTT) up a mountain. There are also 5 high mountain summit finishes. So while ITT performance is important, it was always going to be a rider's climbing prowess and their power to weight ratio that dominated this Giro.

What is interesting with this race though was the inclusion of the MTT, giving us a chance to directly compare riders' flatter ITT and MTT performances.

Both the individual TTs arrived fairly deep into the contest, with the ITT on stage 12 and the MTT on stage 19. I thought it interesting to plot the relative performance of the top GC riders in each of the time trials (click on the pic to see a bigger version). I chose the top 25 on GC (after Stage 19's MTT) as these are the riders more likely to be actually competing on such stages, rather than holding back somewhat to save the legs as much as possible for other duties or race ambitions.


The dots represents each of the top 25 riders on GC after Giro Stage 19. The top 10 riders are highlighted with red dots and text.

The rider's time for the Stage 12 ITT is plotted on the horizontal axis versus their time in the Stage 19 MTT on the vertical axis. e.g. we can see Uran's time in the ITT was a bit over 57:30, and in the MTT a little over 1:07.

When plotted this way we can see whether riders fared relatively better in the flatter ITT, the MTT, or if they performed relatively similarly in each. Of course the further a rider's dot appears to the bottom left indicates faster TT times overall.

The further away the rider's dot is from the diagonal line indicates a dominance of either the ITT (upper left) or the MTT (lower right). If their dot appears close to the diagonal, it indicates their relative performance for the two time trials was balanced.

Those in the upper/left side of the chart are more skewed to perform better in flatter ITTs, and hence their power to aero drag ratio is relatively better than their power to weight ratio, while those in the bottom right side of the chart performed relatively better in the MTT and so their power to weight ratio is relatively better than their power to aero drag ratio.

This Giro is clearly one for the climbers over the TT men given there is an MTT and 5 high mountain summit finishes, and only one (not totally flat) ITT and one TTT.

The balance between each of these two key attributes will play a factor in a rider's likely chances of success in any grand tour and which side of that balance is more dominant depends in large part to the make up of the critical stages. It also points out what element of performance a rider may need to look at in order to improve their overall standing relative to their opponents.

Looking at the chart, there are some riders that would do well to refine their ITT performance, something that's more possible to address with a focus on aerodynamics. Losing weight and gaining power is much harder for a top Grand Tour GC rider to (legally) achieve.

Aru, Rolland and of course Quintana will be dominant riders for the future if they are able to improve their power to aero drag ratio. Of these three, I'd say Rolland and Quintana have the most to gain from aero refinements.

Pierre Rolland
image: velonews.competitor.com
Fabio Aru
image: www.gettyimages.com
Nairo Quintana
image: www.gettyimages.com



Read More......

Thursday, February 06, 2014

Sands through the hour glass

A couple of charts for a bit of fun.

Recently we read about 102 year old Frenchman, Robert Marchand, who last week set a new best distance of 26.925 kilometres for the hour at the new velodrome in Saint-Quentin-en-Yvelines, France. It was widely reported in many journals and blogs. Here's a link to cyclingnews.com item but a quick Google search will show lots of reports. Chapeau to Robert!

Having been involved with a number of age group category hour records, I thought I'd chart all the current records, including the two outlier points of Marchand, and Chris Boardman.

Here they are in table form with details as at February 2014:



I included Chris Boardman's record in the men's list for reference, and because it was set using the then pursuit bike set up rules which are the rules that masters age category records are run under (although those rules have been modified somewhat since Boardman's phenomenal ride).

I note however that our famous centenarian used a regular (Merckx-style) bike set up, but let's not be overly concerned with that. Being upright, let alone riding is super stuff at that age!

Here are all the age group record holders plotted showing age and distance covered in the hour. Click on the pic to see a larger version.


For some added fun I drew a line linking Boardman's and Marchand's records. The slope is just a touch under 400 metres less per year of age. With the exception of the younger masters age categories up to about 40/45 years, the men's records seem to roughly follow that level of performance decline with age, perhaps with a decline closer to a metre per day of age.

There are fewer masters women's records and none past 66 years old, so it's harder to say if their rate of performance decline is comparable, so while eye-balling suggests the rate of decline is less severe than for the men, I'm not sure I'd draw too many conclusions from these data. There are so many variables, and as the ageless TV soap used to tell us... like sands through the hour glass, so are the days of our lives.

Read More......

Monday, November 04, 2013

Left Right Out of Balance

One of the more recent features to emerge with on bike power meters has been the reporting of something called "Power Balance". It's meant to provide an indicator of the split in power production between your left and right legs - an indicator of asymmetry in power output. It's a pretty simplistic indicator of what's going on with pedalling forces, and masks over much detail. It's also not all that clear whether it's of much value.

How's your power balance?
Power balance is now available via compatible ANT+ head units paired with power meters that supply power balance data (e.g. some Quarqs, Power2Max, Garmin Vector, Rotor). Other power meters can also provide such data via their own proprietary data recording systems (e.g. SRM, Polar/Look, MEP, Axis Cranks), and of course some indoor trainers have provided similar data for many years (e.g. Computrainer and Wattbike).

So if your Power Balance is reporting as 46%-54%, then it's reasonable to assume that means 46% of the total power output is coming from your left leg and 54% from your right leg. Except that maybe it's not.

So then, what is it really measuring?
Is it important/useful?
And is the L-R power balance data accurate?

What is Power Balance actually measuring?


You see, while some of the more popular ANT+ power meters are each reporting a power balance number, there isn't a standard as to what power balance actually means, and these meters are not reporting the same thing.

There are two main types of power balance data reported (there's actually more but I'm going to leave those others out for now), and which of these a power meter reports depends on where and how the forces are measured. I've decided to give each a name, it's possible others have already done the same and used a different name and quite possibly there are better ways to distinguish between each type. It's also possible I'm wrong with some details, and I'll be (happily) corrected if that's the case.

The issue comes about primarily because different power meters measure the forces at different points along the drivetrain, somewhere along the transmission from the pedals to the rear tyre. The dividing line is whether the measurement is done upstream or downstream of the spindle or bottom bracket connecting the left and ride side crank arms. Upstream means measurement of the forces applied to each crank arm, or to each pedal (or even cleats or shoes), and downstream means measurement of the forces applied to the crank spider, or chainrings, chain, rear cogs, rear hub, wheel or tyre.

You see, the downstream measurement locations cannot distinguish from which crank arm the force is being applied, whereas measurement done upstream on each crank arm or at each pedal can make that distinction (but they must measure both sides independently to do that). Downstream measurement of power balance is therefore split based on a crank's rotational location whereas upstream measurement of power balance is based on which side of the bike the forces have been applied.

1. Downstream power balance
This version of power balance is calculated from the power applied during the time when one or the other crankarm is forward of the bottom bracket, irrespective of which leg or crank arm is applying the forces. In other words, the left side power balance is the net contribution to power from both legs while the left hand side crank arm is forward of the bottom bracket, expressed as a percentage of the total power. Right side power balance of course must then be the same for when the right crank arm is forward of the bottom bracket.

This is the power balance values the Quarq and Power2Max reports, and also what the Computrainer, Wattbike and SRM systems report via their own data systems.

2. Upstream power balance
This version of power balance is calculated from the power applied to either crank arm for the entire pedal stroke. This version of left side power balance is then the net power applied by the left leg only to the left crank arm for the entire pedal stroke. And of course the same applies to the right side.

This is what Garmin Vector, MEP, Axis Cranks etc report.

1. and 2. are not therefore, measuring the same thing, and nor is one necessarily better than the other in its current simplistic guise.

As an excellent demonstration of the differences, Ray on his DC Rainmaker blog did a test showing the live power balance numbers reported from a Quarq (a downstream device) and the Garmin Vectors (an upstream device). Here's a link to the youtube video:

http://www.youtube.com/watch?v=k0i_jV9ygLI

It's quite obvious how much difference exists between these two versions of power balance. That also assumes of course that each was accurately reporting their version of left and right side data. I'll get to that later.

There is a little more to understand with these data, for instance because the cranks are a connected system, then what happens on one side is affected by what's going on with the other. So while we may see net torque and power reported from each each side (be it the upstream of downstream version of power balance), it is still masking what's actually going on. As yet, data streams with sufficient frequency are not available via ANT+ since it's constrained by transmission of data packets at 4Hz. To do that requires alternative means, which is what SRM's torque analysis, Wattbike and some other solutions provide.

Is power balance data important/useful?


In short, we really don't know. I think there will be times when such data may prove to be somewhat helpful, perhaps in assessing things like bike fits, but one needs to be careful with any assumption that achieving symmetry is the objective. It's not. Better performance is the objective.

And then we also need to learn how to interpret the difference between upstream and downstream power balance data.

So let me start by stating something already very well established in scientific study of pedalling.

Asymmetry in power production is normal and everyone will have a different L-R power balance. It's also well established that asymmetry is also variable and will vary with:
  • power output, absolute and/or relative
  • cadence (or torque)
  • fatigue
  • and likely a few other factors such as bicycle position, seated v standing and so on
Here are just a handful of links to study abstracts to emphasise this point about asymmetry being both normal and variable:
http://www.ncbi.nlm.nih.gov/pubmed/979569
http://www.ncbi.nlm.nih.gov/pubmed/10460126
http://www.ncbi.nlm.nih.gov/pubmed/17369798
http://www.ncbi.nlm.nih.gov/pubmed/21055708

There are others that go back to the 1970s but quick link abstracts are not available. This is not a scientific review, but you get the idea.

So, for instance, it's pretty common to see a different power balance at different power outputs as well as at the same power output but at different times during a ride.

So now that you have a power balance number and a trace of how that balance varies during your rides, what now? I mean we all have such asymmetries, some of us more than others, and yet it doesn't always appear to be a significant impediment to performance improvement, certainly not in my own case of a sizeable acquired pedalling asymmetry as shown in this item, but perhaps I'm the exception and not the rule.

Some asymmetries we might be able to address, and some we might not. Of those that we can, should we be concerned with them? Like I said, I'll leave that question open for others to address but it is my view that we should really only be concerned with those that will demonstrably lead to an improvement in performance, and I'd consider a reduction in potenital for injuries as an improvement (not that I am in any way implying there's an established causal link between power asymmetry and injury).

So far we really have no strong evidence either way to know whether this infomation provides us with any actionable intelligence. And so we progress instead with anecdote, personal experience and experimentation, belief, and all the biases and lack of controls that go with it. Anecdata if you will. Over time I'm sure better information will arise as more research is conducted into pedalling biomechanics.

For now, I'd put power balance data into the category of a curiosity, of limited practical value until some better research is conducted into its use and validity.

Accuracy


Another factor to consider is accuracy of the left-right power data. Don't just assume your shiny new Vectors are accurately reporting power balance or that your Computrainer spin scan data is correct either.

As yet, there really hasn't been much in the way of an assessment of the accuracy of left - right power data, nor for that matter any investigation of the accuracy of many power meter devices in the scientific literature for quite a long time. Please direct me to any if I've missed them.

Downstream power balance data
I would say that the downstream power balance data from a Quarq, Power2Max etc is quite likely to be about as accurate as the total power reported. This is because the same set of strain gauges are used to measure and parse the forces, and all that's required is a means to establish the crank's postion each revolution. Even so, this could use verification, and something as simple as checking the variance in left and right side static torque measurements can provide some decent clues.

Nevertheless, we also know that some ANT+ head units and meters often suffer this tendency to falsely repeat 2-3 seconds of power values when you stop pedalling, and these ghost power readings can readily result in quite sizeable discrepencies in overall power accuracy. Are such false power readings also affecting power balance calculations? If you tend to stop pedalling on one side more than the other, it may well be that such power ghost data is mostly attributed to that one side. I really don't know.

Upstream Power Balance data
The left-right upstream power balance data from a Garmin Vector could well be brilliant or it could conceivably be out by some margin. The other day I saw someone post on Facebook some ride data from their new Vectors. Nearly three hours of solid riding with a 61%-39% L-R power balance, and they were inclined to actually believe it. Knowing the rider, I know his asymmetry is not even close that level.

We already know from DC Rainmaker's blog review the accuracy of the Garmin Vector is affected by how tightly the pedals have been installed. This is summarised in this chart showing how the Vectors Ray was testing reported power relative to other power meters when they were installed into the cranks with different tightness:

Vector's accuracy as a function of how tightly the pedals are installed into the crank arms.
Chart from DC Rainmaker's blog

Given the total variance in reported power for both pedals can be of the order of around 10% depending on how tightly the pedals were installed, then I can readily imagine a large bias error in reported pedal balance would be very easy to create if each pedal is tightened differently.

Indeed it's quite possible a bias error already exists even if both pedals are installed to specification, simply because you have two separate measurement devices, each with its own error range.


So, even if you consider power balance data is of value, you'll need a means to verify its accuracy, as well as understand the difference between upstream and downstream power balance, lest you make poor decisions about a training or positional intervention.


Never fear, you could always wear a power balance bracelet and solve all your problems.


For those that are not aware, it's a forum custom that pink font indicates sarcasm.

Read More......

Monday, October 21, 2013

Crash test dummies

Following my Aero Testing for Dummies post the other day, I've been getting questions about aero testing services and when people can start getting tested, as well as general interest in progress with the project. I won't go into business plan detail but will post casual updates here every so often, and eventually when it's ready for full professional service delivery, I'll update our website (this is a primarily a personal blog, not a commercial one).

This is a sample of the comments:

Sounds like a terrific service. Good for you Alex, am sure it will be a big hit. Be cool to incorporate with a 'dynamic bike fit' service too - make a change to bar drop/saddle height etc, do a lap while you test comfort and aerodynamics. 
It's right up my alley - am trying to think of an excuse to get back to Sydney now.

This technology and service is a perfect complement for bike fit services.

I have no personal desire to do professional bike fitting, I'd rather provide aero test consulting services to professional fitters and/or work in tandem with them. Indeed I'd prefer a bike fitter be involved, so they can learn about the impact of their fitting and equipment decisions on the rider's aerodynamics, power and speed, and make the adjustments with the benefit of my analysis, feedback and advice. I'm sure over time they will get better for seeing such information, as will I.

I can't say much about what's in the pipeline but I expect the system may well ultimately integrate with professional fitting tools so that rider/bike fit and aero data can be managed for ongoing reference and development.

And similar to bike fitting, much of the quality comes with the knowledge and professionalism of those providing the service. The tools are an enabler and/or help with efficiency. The difference with this tool is the results are immediately apparent, objectively measured and precisely quantifiable.

Next up for me is what I've called Phase II - Demonstration testing

This is where I'll do some properly controlled testing over next month or so, but the emphasis will be on nailing the process, getting good aero results and giving people the opportunity to see it in action, and not so much on commercial considerations beyond refining operational processes for efficient use of testing time.

I already have some crash test dummies lined up.

Once I am satisfied with that I'll move to full professional service delivery, and provide some clearer guidance on services and pricing.

I'm hoping to get to Melbourne at some time before long and there's reasonable a chance I might be heading to Tour of Bright to work at the race and perhaps I could do something at the Wangaratta track around that time if anyone is about and logistics can be arranged - but that's just a thought bubble for now.

Read More......

Saturday, October 19, 2013

Aero Testing for Dummies

Just lately I've been having some fun with the Alphamantis aerodynamics testing system here in Australia.

In a nutshell, this system enables me to precisely assess changes in a rider's aerodynamics in real time while they are riding their bike.

The rider does not need to do anything special other than ride their bike around a suitable track. Any regular oval-like cycling track or velodrome will do, although an indoor velodrome is preferred as environmental conditions are far more predictable indoors and of course you won’t get rained out.

All that's needed is an ANT+ power meter and speed sensor on the bike, and a clear track to ride around, one where the rider can maintain position and does not need to brake.

Do a handful of laps, and we have your CdA baseline number. Then make a change to your bike position or change a piece of equipment (e.g. helmet or wheel), do a few more laps and we can tell immediately if you are getting an improvement, and by how much. Lather, rinse, repeat.

Test while riding, know if the position is rideable, how it feels at race pace, as well as whether or not it is faster for the power you have, and by how much.

Simple.

Here's a 7-minute long video showing a sample of it in action, with me explaining in voice over.



That's just a sample of the data capture, there are lots of other things but that's the essence of it.

I've been in a systems testing phase these past couple of weeks, and have successfully tested the system with two riders using different power meters (one an SRM, the other a Powertap) at the Dunc Gray Velodrome. Apart from Rod, who's data was featured in the video, the other rider was my mate Tony. It was only a systems test, not a properly controlled aero test, nevertheless we were able to quickly discern for Tony a difference between two good aero helmets.

The next phase will be to demonstrate for those interested in seeing it in action, in particular those with a professional interest in aerodynamic related cycling performance improvement such as bike fitters, coaches, squad development people, and organisations that have tracks. Australia has over 90 velodromes/tracks to choose from!

The system is portable, meaning I can set it up anywhere with a suitable track, so if there is sufficient interest and access to a clear track, I can travel. All I need is access to a regular 240V power outlet and maybe a table and chair for convenience.

How it works:

Power and speed information from your bike's ANT+ device is transmitted wirelessly to special software on my laptop which, along with various parameters (e.g. rider morphological data, track geometry data, rolling resistance and environmental data) and track timing tape data, calculates and plots charts of power output, speed, CdA, exact track position and so on. It does all this in real time.

There are lots of calculations going on underneath (viewable if desired) such as centre of mass speed, lean angles, precise lap distance actually ridden and so on. And more work is being done to further refine the already sophisticated physics modelling, e.g. modelling the intra lap variation in rolling resistance/tyre scrub, as well as integration with individual track timing data systems for even more frequent precise positional data.

The system also works with the Alphamantis "aerostick" device that can additionally capture the relative wind speed and yaw angles, enabling the software to parse out the effects of any wind during testing.

All the data is also captured for reporting, additional analysis, as well as replaying the data to the rider afterwards if desired.

It is, very, very cool.

Read More......

Monday, October 14, 2013

Power meter usage on the rise at Kona

The Kona World Ironman Championships is over for another year. As part of event registration, the organisers do a count of equipment choices, and this includes power meter brand if fitted to a competitor's bike.

So just for fun, I thought I'd look at the prevalence of power meter usage by Kona competitors for the last five years, including this year. I managed, with a little help from the wattage forum and Google, to locate the data and compiled them into table and chart form. Click on the images to see a larger version.



So while competitor numbers at Kona increased by 36% over the five years 2009-2013, the number of power meters installed on competitor's bikes over that same period increased by 174%!

We can see three major power meter brands: SRM, Powertap and Quarq, have dominated the Kona power meter landscape to date, with Quarq in particular showing strong growth over this period.

Power2Max have begun to make inroads in recent years, and we can also see the emergence in 2013 of newer power meter offerings from Rotor, Stages and Garmin. The old Polar power meter is a distant memory, and ergomo usage never really got going, although a few souls were still using them up to 2012.

It appears the overall solid increase in usage of power meters by those competing at Kona has largely been satisfied by uptake of newer power meter brands. It would be risky to assume this translates directly into general market trends for power meter usage but it certainly provides a good snapshot of the trends for Ironman athletes.

The data on total bike numbers and power meter counts were obtained from these website links by Lava Magazine (2010-2013) and Triathlete Magazine (2009):

2013 Kona IM Bike Count
2012 Kona IM Bike Count
2011 Kona IM Bike Count
2010 Kona IM Bike Count
2009 Kona IM Bike Count

Links were active and  available at time of writing this post.

Read More......